keep if agency_id== 2 // keep only Freddie
keep if prop_type_id == "SF" // single-family house only

keep if orig_ym >= ym(2009, 9) // keep only the period when ltv > 105 was eligible for HARP
keep if orig_ym >= ym(2012, 1) // keep only the period when ltv > 105 was eligible for HARP

keep if occ_stat == "P" | occpy_status == "O" // keep only owner-occupied units
drop if ocltv > oltv // drop those with second mortgages

keep if abs(ltvprev_diff) <= 10

